The present invention was developed in the environment of the fabrication of relatively complex three-dimensional articles made up of multiple layers of relatively thin metal, and in particular such layers of stainless steel. Such articles find utility, for example, as heat shields in automotive and aircraft applications. In the fabrication of such articles, since the shapes are relatively complex, cutting and welding must occur in three dimensions and involve many turns, bends, and the like. In addition, such articles often have entrapped areas which can be filled with insulating material, such as fiberglass, and it is necessary to provide improved means to fabricate such articles. There are sometimes only two layers to be cut and welded, and sometimes three or four layers. Because of these different thicknesses and other factors, complex fabrication techniques are dictated by the shape of the articles.
Prior to the present invention, these parts were made laboriously by hand, by folding over the edges, and then crimping them to make finished edges along the outline of the part. This was highly labor-intensive, and thus correspondingly expensive. In addition, because of the repetitive and mind-deadening quality of this low-level work, the parts were more susceptible to errors and thus rejects than the same parts when made in accordance with the present invention.
The present invention when used in fabricating such parts completely eliminates all of these hand operations having to do with crimping, folding, and bending. The parts are simply assembled, laid up as it were, and then simultaneously cut and welded to produce smooth, finished edges.
In addition, the invention accommodates the fact that the edge portions where the cutting and welding is to take place contains only metal, but closely spaced thereto are areas protected by only one relatively thin layer of metal under which there may be insulating material. The invention must be controlled in such a manner as to not cut into or otherwise diminish the insulating qualities of the insulating portions of the articles being made. This is easily accomplished using state-of-the-art computer-controlled fabricating equipment.
The present invention utilizes very little in the way of new equipment, but rather it is primarily an improved application of state-of-the-art equipment. More specifically, in the prior art conventional manners of cutting metal using a laser, a narrow stream of oxygen is often used. This high speed jet of oxygen is used to literally "blow away" the molten metal created by the laser to thereby make the cut.
On the other hand, in conventional welding using laser energy, a relatively wide stream of an inert shielding gas is used at relatively low pressure in order to be sure that the work site is shielded from oxygen and that no metal is blown away. The molten metal is used, of course, to actually make the weld.
As set forth in more detail below, the present invention utilizes both of these techniques in a unique manner to produce its advantageous simultaneous welding and cutting of sheet metal.
The present invention is to be distinguished from laser technology as applied to the handling of non-metallic materials, especially plastics. The use of lasers in simultaneously cutting and welding plastics has been established; such is not the case with metals.
The present invention, as discussed in more detail below, depends upon the creation of a globule or pool of molten metal, some of which is blown away and the remainder of which is used to weld. Vaporization of this material is generally undesirable since it could widen the cut and result in the creation of rough edges and lack of control of the cutting and welding operation. When working with plastics, the vaporization of the material directly under the laser results in melting of additional material outboard on both sides of the cut, and that melted material can if desired result in some degree of welding while cutting.
Another important difference of the invention as applied to working metal as compared to prior art use of laser technology in working plastic is that the sheets of plastic material to be operated upon must be in tight and intimate contact. If the plastic sheets were not in tight and intimate contact, the heat of the laser would simply cause them to curl inwardly towards each other into the cut created between them and also into the space between the layers. The present invention provides for space between the layers in a controlled manner, and this space between the layers aids in the advantageous manner of operation of the present invention.
The present invention is also to be distinguished from other kinds of prior art in the laser field wherein a smaller piece of material, and it may be metal, is cut off and the remaining end is simultaneously welded in place in a larger piece of material. There are substantial differences in the invention from this technology, primarily that, with these prior art techniques, the edges may not be clean and finished, and the material cut off is treated as scrap. This is not the case in the present invention where there is no scrap as a necessary condition, as described below.